A general method for implementing stereoscopic images (or 3D images) is to emit different images to two human eyes. Stereoscopic displays are mainly divided into glasses stereoscopic displays and glassless (naked-eye) stereoscopic displays according to whether or not it is necessary for the viewer to wear glasses in order to emit different images to their two eyes, respectively.
Especially, projection of stereoscopic images implemented through a large screen as in a movie theater typically uses a polarization method in which left and right images separately pass through polarization glasses having left and right polarization lenses with orthogonal polarization directions. This method implements stereoscopic image projection in the following manner. First, images are captured using two cameras. The images are given orthogonal polarization directions through polarizers and their overlapping images are then displayed on a screen. Then, the viewer views the images captured using the two cameras with their two eyes through polarization glasses.
FIG. 1 illustrates the structure of a conventional dual projector system for stereoscopic image projection.
To provide stereoscopic image projection according to the polarization method, the conventional dual projector system uses two conventional two-dimensional (2D) projectors 1 and 2. One of the 2D projectors 1 emits left images and the other 2D projector 2 emits right images. The left and right images are then projected on a screen 5 after passing through polarization filters 3 and 4 with orthogonal polarization directions. The left and right images overlapping on the screen 5 are then viewed separately by the two eyes of the viewer through left and right image lenses 7 and 8 of polarization glasses 6 worn by the viewer, so that the viewer feels as if they view 3D images.
The conventional dual projector stereoscopic image projection system is very expensive since it uses two 2D image projectors and two polarization plates as described above and also includes peripheral devices. The number of projectors required to project stereoscopic films in a theater is twice the number of the movies since two projectors are required for each movie. The positions of left and right images projected on the screen vary depending on the positions of the two projectors. Therefore, incorrect adjustment of the positions of the two projectors reduces the conformity of stereoscopic images.
Thus, there has been a need to provide a single-projector system for stereoscopic image projection. Systems based on a method of dividing the area of the single projector LCD module and a method of using an LCD shutter has been developed to meet the need.
FIG. 2 illustrates the structure of the conventional system for stereoscopic image projection based on the method of dividing the LCD module.
The conventional stereoscopic image projection system shown in FIG. 2 operates in the following manner. First, light generated by a light source 201 is reflected using a reflecting mirror 202. The reflected light passes through an LCD module 203, which then outputs left and right images with different polarization directions. The left and right images are projected on a screen 205 through a condenser lens 204. The left and right images projected on the screen 205 are separated by passing through left and right image lenses 206a and 206b of polarization glasses 206 worn by the viewer, respectively, so that the viewer feels as if they view 3D images.
The following is a detailed description of how left and right images come to have different polarization directions as light passes through the LCD module 203.
The LCD module 203 includes two polarization films 209 and 210. Each of the polarization films 209 and 210 includes pairs of two regions with orthogonal polarization directions that are alternately arranged in a vertical direction. Specifically, the polarization film 209 includes pairs of two regions, first polarization regions 209a and second polarization regions 209b, and the polarization film 210 includes pairs of two regions, third polarization regions 210a and fourth polarization regions 210b. A beam displaying left images included in the light reflected by the reflecting mirror 202 passes through the first polarization regions 209a of one of the polarization films 209 included in the LCD module 203, while a beam displaying right images included in the light reflected by the reflecting mirror 202 passes through the second polarization regions 209b of the same polarization film 209, which have a phase different of 90 degrees with the first polarization regions 209a, so that the reflected beams displaying left and right images come to have orthogonal polarization directions. Then, as the liquid crystal is driven according to whether or not each image is to be displayed, the emitted left images pass through the third polarization regions 210a included in the other polarization film 210, which have a phase difference of 90 degrees with the first polarization regions 209a, while the emitted right images pass through the fourth polarization regions 210b included in the other polarization film 210, which have a phase difference of 90 degrees with the second polarization regions 209b, so that the left and right images come to have orthogonal polarization directions. Then, the beams of left and right images are projected on the screen 205 after passing through the condenser lens 204. As a result, left and right images with orthogonal polarization directions are alternately arranged on the screen 205. The viewer separately recognizes the left and right images through the polarization glasses 206.
The method of projecting stereoscopic images through division of the area of the LCD module 203 has a problem that the overall resolution is reduced since the projected area is divided into left image projected regions and right image projected regions. That is, as the total area of each of the left and right images projected on the screen decreases, the resolution of each image, which has passed through each lens of the polarization glasses, must be reduced, which limits its application to movie theaters with large screens.
In addition, left and right images must correctly pass through their defined regions. Otherwise, the stereoscopic image quality will be reduced. It is difficult to avoid this problem when left and right images are processed separately in space. When stereoscopic images are projected on a large screen as in a movie theater, it is not easy to adjust the positions of left and right images projected on the screen since small position mismatching at the projector will significantly reduce the conformity of stereoscopic images at the viewer.
FIG. 3 illustrates the structure of a conventional LCD-shutter-based system for stereoscopic image projection.
To overcome the problem that may occur when left and right images are spatially divided in the single projector method, the method shown in FIG. 3 produces stereoscopic image content including alternating left and right images. An LCD shutter 302 is used to cause the left and right images to have different polarization directions.
Specifically, in the method of FIG. 3, left and right images are alternately stored in the content. When a projector 301 emits images according to the content, the LCD shutter 302 is driven to have the same polarization direction as that of left images at the times when the projector 301 emits the left images and is driven to have a polarization direction different from that of the left images at the times when the projector 301 emits the right images. This operation can be performed by a shutter driver 303 which drives the LCD shutter 302.
However, this stereoscopic image projection system using the LCD shutter has a problem that the response delay of the LCD shutter when it is driven causes crosstalk between left and right images. Especially, the time during which alternating left and right images are switched must be short enough to not be noticed by a human. The slow response time of the LCD shutter will be a serious problem when left and right images are quickly switched.
In addition, there is a need to provide a technology for replacing the LCD shutter with different means for increasing the polarization ratio, since the polarization ratio of left and right images of the LCD shutter is not so high.